The present invention relates to an apparatus for generating and detecting an electromagnetic ultrasonic wave which serves to carry out, in connection with a conductive material, the detection of internal defects, the judgement as to the type of a material and thickness measurement.
For performing the measurement concerning internal defects or the like, an ultrasonic measuring instrument and an electromagnetic ultrasonic measuring apparatus have been utilized. However, in order to use an ultrasonic measuring instrument provided with an ultrasonic vibrator of quartz or barium titanate, a material to be measured is required to have a smooth surface and water or oil for receiving an ultrasonic incident wave is necessary. Thus the usage of the instrument has been remarkably restricted under an unfavorable surface condition such as the presence of rust or a high temperature condition.
An electromagnetic ultrasonic measuring apparatus was known and disclosed in the Japanese patent publication No. 24867/1969. It has been generally considered that the realization of the practical usage of the apparatus is almost impossible since any conventional apparatus fails to provide an adequate efficiency in electromagnetical generation or detection of an ultrasonic wave and tends to produce a broad dead zone due to the occurrence of the magnetic induction between an ultrasonic wave generating coil and a detecting coil, thus causing the apparatus to be inoperative in a case where the thickness of the material is thin and the internal defect is located near the surface of the material. Generally, in an apparatus for generating and detecting an ultrasonic wave, a magnetic field is formed near the surface of one side of a conductive material and an eddy current is also generated therein by providing an ultrasonic wave generating coil to which a high frequency current pulse is supplied, to thereby cause the interaction therebetween to occur and the ultrasonic wave traveling in the material to generate and further, the eddy current generated in the surface area as a result of the interaction between the ultrasonic wave and the magnetic field is detected by a detecting coil which operates in accordance with the electromagnetic induction theory.
The detected signal obtained by the detecting coil in such electromagnetic ultrasonic measurement includes a transmission pulse or induction signal induced by the high frequency current pulse passing through the ultrasonic wave generating coil and a reflected echo consisting of the ultrasonic wave which is reflected within the material. The time zone covered by the transmission pulse is called, in an ultrasonic defect inspection, a dead zone due to the transmission pulse, which prevents the recognition of the presence of a reflected echo and preferably must be reduced.
Further, it has been desired to improve the detection sensitivity since a conventional electromagnetic ultrasonic measuring device produces a detection signal with poor sensitivity.